Field of the Invention
The present invention relates generally to a valve for viscous fluid applicators.
Many packaging applications require the application of adhesive to flaps for sealing packages. In some cases in which a liquid adhesive or glue is used, valves are used to dispense the glue for application to the packages being sealed.
One dispenser for use in dispensing viscous fluids, such as hot melt adhesives, is disclosed in U.S. Pat. No. 5,875,922. The dispenser includes an armature mounted within a fluid chamber for reciprocating motion relative to a pole member. The armature is adapted to permit the hot melt adhesive to flow through and around the armature as the armature is moved towards the pole member.
However, the interface between the armature and the pole piece is located near the center of the solenoid coil. Consequently, the fluid chamber extends within the interior of the solenoid, and a portion of the armature extends half the length of the solenoid coil. The additional length required for the armature, results in increased mass for the armature. Moreover, fluid flow paths through and around the armature are lengthened. Moreover, sealing between the fluid chamber and the solenoid coil must be provided around coextensive portions of the solenoid coil and the armature.
Thus, the dispenser includes an elongated tube which is interposed between the armature and the dispenser body to provide sealing for the fluid chamber. The sealing tube is made of a heat resistant, non-magnetic material, such as stainless steel. The sealing tube produces a long air gap between the armature and the valve body, with the sealing tube located in the air gap substantially the entire length of the armature. Consequently, the magnetic force used to drive the armature must be large enough to compensate for the losses due to the presence of non-magnetic sleeve in the air gap.
A further consideration is that viscous fluid dispensers of this type preferably must be adapted to permit adjustment in the stroke of the armature due to allow some leeway in manufacturing tolerances. In the dispenser disclosed in the '922 Patent referenced above, the gap between the armature and the pole piece is adjusted by turning the pole piece which is threaded into the body.